Phospholipases A2 (PLA2) are important cellular enzymes that regulate the maintenance of membrane phospholipid composition and the production of lipid mediators. Increased degradation of membrane phospholipids and decreased levels of polyunsaturated fatty acids in the AD brain are indications that PLA2 are involved in the pathogenesis of this disease. Studies in this Project (Grace Sun, PL) are focused on two types of PLA2: the low molecular weight secretory sPLA2 that is induced by cytokines, and the calcium-dependent cytosolic cPLA2 that is regulated by intracellular protein kinases. The major objective of this project is to examine the roles of these PLA2 in response to the oxidative and inflammatory stress that occurs in the AD brain. Studies will test the hypotheses that Abeta and oxidative agents, including oxidized lipoproteins and pro-inflammatory cytokines, up-regulate PLA2 in neurons and glial cells (microglia and astrocytes), and that lipid metabolites, including arachidonic acid (AA), lysophospholipids and prostaglandins, are important factors in mediating glial cell activation and neuronal degeneration. Specific Aim 1 will investigate the effects of Abeta and lipoproteins on cPLA2 activity in neurons and glial cells, and determine the roles of protein kinase C and mitogen-activated protein (MAP) kinases in the functional regulation of cPLA2. Studies will examine whether cPLA2 is essential for production of AA for prostaglandin biosynthesis. In situ hybridization and immunohistochemical studies will be carried out to examine mRNA and protein expression in AD and age-matched control brains. Specific Aim 2 will investigate the effects of Abeta and oxidized lipoproteins on responses to cytokines in astrocytes and microglial cells, and delineate effects on inducible gene transcription using the microarray technique. Co-culture systems will be used to investigate interactions between neurons and microglial cells or astrocytes, and to determine whether sPLA2 released from glial cells can enhance the degradation of neuronal membranes due to treatment with Abeta and oxidized lipoproteins. Specific Aim 3 will examine whether inclusion of specific lipid metabolites in lipoproteins will modulate glial cell activation and neuronal degeneration induced by oxidized stress. These studies should establish a definitive role for PLA2 and specific lipid mediators in AD pathology, thereby contributing to the development of novel intervention strategies to inhibit the oxidative and inflammatory damage seen in the AD brain.